Recently, a high-speed operation of a semiconductor integrated circuit device is in demand. Such a high-speed operation mainly requires a reduction in size of a semiconductor device such as a transistor, a reduction in resistance of a wiring, and a reduction in dielectric constant of an interlayer dielectric layer. However, the high-speed operation based on such approaches has limitations.
As such, “improvement of a carrier mobility of a channel” is under consideration as a way to realize a high-speed operation. A semiconductor used in the semiconductor integrated circuit device mainly includes silicon (Si). A channel of a transistor is substituted with a semiconductor material having a higher carrier mobility than Si. Silicon germanium (SiGe) or germanium (Ge) is getting a lot of attention as a material of the channel.
For example, Si has an electron mobility (μn)≈1450 to 1600 (cm2/V·s) while Ge has an electron mobility (μn)≈3900 (cm2/V·s). In addition, Si has a hole mobility (μp)≈430 to 505 (cm2/V·s) while Ge has a hole mobility (μp)≈1900 (cm2/V·s).
As described above, Ge has higher electron mobility and hole mobility than Si. For this reason, Ge or Ge-rich SiGe which contains Ge of a high concentration is promising as a next-generation channel material.
One of primary endpoints for the channel material includes a surface roughness. When a surface roughness of the channel material does not fall within an allowable range, even if the material has a good carrier mobility, scattering of carriers is generated due to irregularities of a surface of the material. Thus, such a material may not be sufficient to use as the channel material.
Further, the miniaturization of the semiconductor integrated circuit device has been prompted. As such, even if a surface roughness on the order of micrometer (μm) is sufficiently allowable, such a surface roughness is still too rough, thus failing to meet the order of nanometer (nm). The level of a surface roughness of Ge or Ge-rich SiGe film in the existing miniaturized semiconductor integrated circuit device fails to satisfy the needs of a maker. That is to say, Ge or Ge-rich SiGe film on the order of nanometer (nm) is hard to be formed on an underlayer such as SiO2, SiN, C, metal or the like, with a goof surface roughness.